BACKGROUND: Diagnosis of Spontaneous Bacterial Peritonitis (SBP) depends mainly on ascetic fluid culture which may be negative in spite of the clinical suggestion of SBP and high ascetic fluid neutrophilic count. AIMS: This study aimed to evaluate the biological importance of amyloid A biomarker in both serum and ascetic fluid to diagnose SBP as early as possible and to compare it to other markers (C-reactive protein (CRP), and the neutrophil-to-lymphocyte ratio (NLR)). METHODS: This study included 37 patients with hepatic ascites; twenty-two of them had SBP, and 15 patients did not have SBP. Serum and ascetic fluid amyloid A, ascetic fluid neutrophil, C-reactive protein, and neutrophil-to-lymphocyte ratio were measured in all subjects before the start of antimicrobial chemotherapy to the infected ones. RESULTS: Both the serum and ascetic fluid amyloid and also, CRP were significantly higher in patients infected with ascetic fluid than others. The cut-off point of serum amyloid A for early detection of SBP was 9.25ug/ml with the high sensitivity and specificity. For ascetic amyloid A, the sensitivity and specificity were 90.09% and 60% at cut-off point 2.85ug/ml, respectively. CONCLUSION: Amyloid A in serum and ascitic fluid can be considered as a good biomarker for early diagnosis of SBP.